The administration of oxygen to a patient usually has an adverse drying effect on the patient's respiratory system. Therefore, various humidifying devices have been used to humidify and heat the oxygen being administered to a patient by mixing the oxygen with vaporized water.
A typical humidifier system for inhalation therapy comprises a bottle or the like reservoir containing a sterile liquid such as water, and a humidifier assembly. The humidifier assembly is usually connected to a supply of pressurized oxygen. A heater associated with the humidifier assembly vaporizes the liquid in the bottle and the vaporized liquid is admixed with the oxygen in the humidifying assembly to produce a humidified and heated oxygen stream which is delivered to a patient through an outlet in the humidifier assembly.
A drawback associated with the humidifier heater is that if the oxygen flow to the humidifier is reduced or inadvertently interrupted, the heater has a tendency to provide too much heat to the liquid in the reservoir thus causing the overheating of the liquid and the breathing gas and creating a hazardous condition.
My U.S. Pat. No. 4,911,157 discloses a system for nebulizing and heating a breathing gas in which the heat input to the supply gas is automatically adjusted in response to a change in the volumetric rate of the supply gas so as to avoid any overheating of the breathing gas.
My nebulizer system includes a nebulizer module, a heater module provided with an annular heat transfer element secured to the nebulizer module, and a liquid receptacle removably attached to the heater module. The nebulizer module is connectable to an oxygen supply source, and through an outlet, to an inhalation apparatus. The nebulizer module includes a nebulizing chamber where pressurized oxygen gas, ambient air, and water are combined to form a conically shaped aerosol spray which, in turn, impinges upon the annular heat transfer element operably associated with the heater module. Those particles of the aerosol spray which impinge upon the heat transfer element are volatilized to provide the desired amount of latent heat to the oxygen mixture passing to the patient.
The total flow from the nebulizing chamber may be modulated by the amount of air introduced into the nebulizing chamber. As an example, total flow with no air entrainment averages approximately 7 liters per minute. This flow increases geometrically as the oxygen concentration is diluted by air so that at full air entrainment, the total flow approximates 80 liters per minute. Clearly, not as much heat is required to volatilize the aerosol spray at zero entrainment (pure oxygen) as at full entrainment; thus, the heat output requirement of the heat transfer element can vary considerably.
My nebulizer system provides a self-regulating heat input feature which mitigates the problem of changing heat requirements. By providing substantial axial alignment between the annular heating element and the throat of the nebulizer assembly, the heat output of the heating element is self-regulated as a function of the conical flow pattern exhausted from the throat. Because a smaller flow cone is exhausted from the throat as the entrainment of the nebulizer is reduced, fewer aerosol droplets are impinged upon and vaporized by the heat transfer element. Conversely, as a larger size flow cone is exhausted from the throat as a result of higher entrainment and, thus, increased total flow, more particles strike the heat transfer element. Therefore, the aerosol spray can be maintained at a substantially constant temperature at widely varying air intake rates to the nebulizer system. As such, a greater heat input to the gas stream is automatically provided to match the higher flow rate.
Although my self-regulating nebulizer is suitable in most inhalation therapy applications, there exists applications where a humidifier is more suitable than a nebulizer.
What is thus needed is a humidifier system using a similar heating technique and which, like my nebulizer system, is capable of providing and maintaining an adequate output of breathing gas having a regulated humidity level and temperature with relatively low compliance and relatively small dead space volume.